Letter to The Avon India Rubber Co. Ltd. clarifying tyre testing methods, slip angles, and correcting previously sent rim width data.
| Identifier | ExFiles\Box 156\3\ scan0053 | |
| Date | 3rd May 1938 | |
| 1331 Rm {William Robotham - Chief Engineer} /FJH. {Fred J. Hardy - Chief Dev. Engineer} 1/MH. {M. Huckerby} 3rd. May 1938. Messrs. The Avon IndiaProduction 20 HP. with 4-speed box and Front Wheel Brakes Rubber Co. Ltd., Melksham, WILTS. For the attention of J.G.Mackay, Esq. Dear Sirs, With reference to our method of testing tyres on our skid pan, we obtain the slip angle by subtracting the telescope reading for zero speed (actually 4 m.p.h.) from the telescope reading for the speed concerned. Thus, in the case of the IndiaProduction 20 HP. with 4-speed box and Front Wheel Brakes 6.50 x 17 6 ply tyre, average reading at zero speed = 0° 37' average reading at 20 m.p.h. (19.4 m.p.h. on speedometer) 2° 27'. Therefore slip angle = 2° 27' - 0° 37' = 1° 50'. In connection with the sideways acceleration we aim at testing all tyres at true speeds of 20 m.p.h., 25 m.p.h. and 30 m.p.h. The speedometer on the particular car used when you visited us was correct with 5.50 x 18 tyres. On other tyre sizes we made the tests at the speeds shown on the table of results in order to maintain the true speeds of 20, 25 and 30 m.p.h. As the sideways acceleration depends only on speed and radius the figures obtained on Fisk tyres apply equally to other tyres at the same true speeds. We agree with your assumption that an Avon 6.50/16 6 ply Duotread tyre should have more cornering power than the similar 4 ply tyre. We find that there is a mistake in the results we sent you concerning the width of rim used. On the table of figures and the curves we stated that all rims were 4.500 wide. Actually all 16.00" dia. rims were 4.500 wide and all 17.00" dia. rims were 4.000 wide. Will you please alter these particulars on your copies of the results. | ||
From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).